Means for reducing interference in electrical circuits



20, 1931. K. LUTOMIRSKI MEANS FOR REDUCING INTERFERENCE IN ELECTRICAL CIRCUITS Filed April 26. 1928 2 She ets-Sheet 1 Oct. 20, 1931. K. LUTOMIRSK! 1,828,503

MEANS FOR REDUCING INTERFERENCE IN ELECTRICAL CIRCUITS Filed April 26. 1928 2 Sheets-Sheet 2 ATTORNEY Patented Oct. 20,

UNITED, srA T s PATENT OFFICE KAREL LUTOMIBSKI, OF YORK; N. YJ,

ASSIGNOR TO BELL TELEPHONE LABORA- TORIES, INCORPORATED, OF NEW YORK, Y.; A CORPORATION OF NEW YORK MEANS FOR REDUCING- INTERFERENCE IN ELECTRICAL ornourrs Application filed April 26,

This invention relates to electrical transmission ClICLlltS and particularly to means for preventing disturbances in the operation of such circuits.

Another and a more specific object is to v prevent interference between the operation of space dischargev devices, the filaments of; which are electrically connected or are energized from a common current source, by reducing or preventing potential disturbance in the circuit of one device due to stray or:

leakage currents from the circuit of another of the space dischar e devices.

It is frequently esirabl'e to filaments of a plurality of electron tubes in the same telephone repeater or in separate telephone repeaters from a single potential source as by connecting the filaments of the tubes with a source of energizing potential, such as a grounded direct current battery. In such cases, it has been found-that the portion of the output currents, such as speech. currents, of each tube which isfed back through ground to the common filament circuit will cause objectionable: disturbances,-

commonly known as cross-talk, in the output of the other tubes.

in the prior art to mlnimize this cross-talk by effectively neutralizing the effects of the fed-back currents. Applicant has discovered that the principal source of cross-talk trouble in certain typical systems is stray current transmitted from the output of one electron tube through the output transformer therefor to the filamentcircuits of the other electron tubes through leakage paths such as ground or other connections.

r In one embodiment of the inventiom this:

latter type of interference isminimizedby reducing the amountof stray current transmitted from the output of one electron. tube energize Means have been adopted 1928;; Serial No. 273,078.

through-theoutput transformer therefor and leakage or other paths to the filament circuits ofthe othertubes. In a preferred emr l e f bodiment of the invention this reduction in An object of the invention is to reduce interference between neighboring transmis- I sion circuits or, apparatus due to undesired the feed-back currents is obtained by using an output transformer for a tube or repeater having such a structure that the capacities between the windings ofthe transformer and between the windings and ground are very low, and such that these capacities are 10- taken in, connection with the accompanying drawings in which:

Fig. 1 shows diagrammatically one way in which cross-talk interference occurs between neighboring transmission circuits;

Fig. 2 shows how a transformer of the system of Fig. 1 may be modified in accordance with the invention to minimize the crosstalk interference therein; I i

Fig. 3 shows diagrammatically one way in which cross-talkinterference occurs between electron tubes energized from a common source, in thesame or different telephone repeaters; I i V 4; shows vhow the hybrid coil transformers in the repeater circuits of Fig. 3

may be modifiedto minimize the cross-talk" interference therein; and V Fig. 5 shows inmore detail the construction of the modified transmission devices of Figs. 2 and 4. I

Referringto Fig. 1 two neighboring electrical circuits L and L which may be, for example, telephone lines, are shown. The circuit L 'comprises a primary portion 1 connected to a source of alternating current indicated by the alternating current generatorfl, and a secondary portion 3 connected to a load circuit indicated by the resistance 4:. The primary'and secondary portions 1 waves such as a'subscribers signaling circuit,

and 3 of circuit L are coupled to each other so as to obtain efiicient transmission therebetween by a transmission device having inherent capacity eitects or leakage between its elements which are at different potential,

such as the transformer 5 havinga primary winding 6 and a secondary winding 7"with mutual capacity therebetween, connectedto the portions 1 and 3 of circuit L respectively. The circuit L may also be utilized for transmitting electrical waves from a source (not shown) to a load circuit indicated by the resistance 8.

It is assumed that the two circuits L and L are relatively located, as is often the case,-

so that the circuit L is coupled tothe sec ondary portion 3 of circuit L through a leakage or capacitive path, as indicated. by the dotted condenser 9, and so that the primary portion 1 of circuit L is connected directly to circuit L as by an electrical conductor or a common ground (such as might be obtained if these circuits comprise grounded transmission apparatus), or indirectly through leakage or capacitive paths for. alternating currents from the respective circuits to ground, as indicated by the dotted 'I condenser 10 between circuit L and ground former 5, through the capacitive path be tween windings 6 and 7 to secondary windin g 7, the lower wire of the secondary portion 7 8 of line L capacitive path 9, the upper wire of circuit L load resistance 8, lower wlre of circuit L capacitive path 10 to ground,

capacitive path 11 and primary portion l of circuit L to primary winding 6 of transformer 5.

Applicant has discovered that prior art res peating coils or transformers, suchas transformer 5, inserted in a system such as il'-' lustrated in Fig. l have such mutual capacitybetween the windings thereof and between the windings and ground as to allow leakage alternating current of considerable magni-.

tude tobe transmitted through the capacitive paths, which leakage will be transmitted over the leakage or capacitive paths between circuits L and L and cause ob e.c-'

tion able interference or crosstalk."

This interference or cross-talk may be reduced or substantially eliminated in accordance with the invention by utilizing in the system of Fig. l repeating coils or transformers constructed so as to have low mutual capacity between windings and between the windlngs and ground, such as for example. the specially designed transformertiillus trated in Figs. 2 and '5.

Referring to Figs. 2 and 5, it will be seen that transformer 5 comprises a multi-layer primary winding 6 and a secondary winding 7 respectively wound on different legs of the shell-type core 13. The secondary winding '7 may comprise a single layer only, but the primary winding 6 has two or more layers superposed on the core comprising in the caseil-lustrated aninner layer lt nearest thecore and farthest from the secondary winding 7, an intermediate layer 15, and an outerlayer 16 farthest from the core and nearest the secondary winding 7.

By winding. the primary 6 on the core in superposed layers as illustrated in Figs. 2 and '5'so that only a portion of its turns are adjacent the secondary winding 7, the effective mutual capacities between these windings are reduced. This, effectively reduces the amount of leakagealternati'ng current which will be transmitted over the capacitive path from the primary portion 1 to the secondary portion 3 of circuit L and thus the amountofjstray alternating current transmitted from circuit L1 to circuit L over the capacitive path 9,

The effective leakage of alternating current from the high potential layer 1% of primary winding 6- to ground may be also minimized by increasingthe distance between that'layer and" the core 13, by inserting the core l S iir-a metal case (not shown) and spacing it'-10r insulating it from the case so that theefi ecti've capacity between core and case is low, or by locating a part of the lower potential'layer16,bet-ween the higher potential layer 14 and the core to effectively shield the latter layer from the core.

Thee'fi'e'ct-ive difference or" alternating currentxpotential 'betwecn windings 6' and 7, and thus the transfer of stray alternating currents from circuit L to circuit L over the path d'escrib'ed above may be also reduced in accordance withthe invention, as shown in F igs'. 2 and 5 by connecting the layer 14 of primarywinding 6, which is farthest from the secondary winding 7, to the terminal of the source of alternating current 2 which has the highest alternating current potential with re spe'ct to secondary winding 7, and the layer 16 of primarywinding 6, which is nearest the secondary winding 7, to the terminal of source 2-whichfis at a lower alternating current potential with respect to secondary winding 7'. this means, the secondary winding 7 is shielded from the high potential layer 14 of primary winding 6 by layers 15 and 16 of primary winding 6, which layers are of lower potential than layer 11. The effective transfer of energy over the capacity path betweenwindings 6 and 7 and between theportions land 3 of circuit L is thus minimized."

Anyone of the ,above' described methods or any desired-combination of them -or any designing thetransformersin the system of Fig. 1 to reduce the 'le'akage of alter-nating' currents between the circuits L [and to such a low value that it will not cause objectionableinterference in the operation of these circuits.

In Fig. "3'are phone repeaters R and R which are ofthe well known two-way, two-element or 22-type. Repeater R comprises 'tw'o t'woway transmission line sections 17 and 18 which are terminated in the usual balancing networks N which simulate the impedance of the line. The line sections 17 and 18 'are asso'ciated'by means of hybrid coil transformers 19an'd 20 in a manner well kIlOWIllIl the; art -w1th an amplifying device 21 forimpressing on line section 18 in amplified form "signals from line section 17 and with an amplifying device 22 tor impressing online section 17 in amplified form signals fromline'section The hybrid coil transformer 19 comprises. the j usual series winding 19 and the line wmdm'gs 19 and the hybrid coil transformer 20 a series winding 20 -and line windings 20 The input circuit of amplifier21" is connected across bridge points in line section 17 between line windings"19 through the gain adjust ing potentiometer 23,whichhas its mid-point. grounded, and input transformer 24, and the output circultot amplifie'r23 isco'nnected tothe series-winding 20 of hybrid 'coiltransformer 20. Similarlyfthe input "circuit of amplifier 22 is connected across bridge points in line section 18 between linewindings 20 through thegain adjusting potentiometer 25, which has its mid-point grounded, andlnput transformer 26, and the output circuit of amplifier 22 is connected to theseries winding 19 ofhybridcoil19.'

' The amplifiers 21 and 22 maybeof any desired type, but'three electrode-Vacuum tube amplifiers are. illustrated, amplifier 21 including a cathode or 28 and acontrol electrode or 'grid29'and {am-- plifier 22 similar electrodesdesignated, re spectively 30,31and32g The repeater R2 as illustrated has elements which are identical with those of repeater R which has been described, theseelements being respectively, p 7

27, 30 of amplifiers 21and 22, respectively,i

designated withsimilar characters, but with the addition of aprime'(') rnar The filaments 27, 30' of'am of repeater R and the filaments of repeater R are connected-in series'i-n' a c1'rcuit supplied with heating current from a common battery 33 through a retardation coil 3 1. The anodes 28,31,28, 31 of amplifiers 21, 22, 21and 22,respectively, are connected through retardation coils 85, 36,37 and 38, respectively, to a common plate current supl lybattery 39.

The balancing condensers inthe individual with respect to filament 27,'an anode or plate filamentleadsfof the amplifier tubes arelutiv set up across the filament circuits of these,v

tubes, whichin turn wouldcause cross-talk disturbances in the .other tubes having fila X ment circuits in common with the disturbing shown two-neighboringteletheamplifier tubes 21, 22, 21 and 22, respectively, are maintained at negative potential the filaments of the tubes by means of individual. C batteries inserted between the filaments and the grids. As usual in suchv circuits the common filament circuit ofthe amplifier tubes is connected to ground at some convenient point, such as point 41.

'Toshow how crosstalk interference may arise-in the repeater system just described, it will be assumed that signal variations are being received over transmission line 1 17. These variations will be transmitted through the bridged connections of hybrid coil 19 and impressed through gain adjusting potentiometer 23 and input transformer 24 on the input circuit of amplifier tube 21. The amplified variations in the output circuit of amplifier tube 22 will be impressed on line section 18 through the inductive coupling between the series winding 20 and the linewindings 20 ofthe hybrid coil 20.

' Ithas been found that in such a repeater 1 circuit, because of the mutual capacity effect present between'the series'winding 20 and the line windings 20,; ofhybrid coil 20, all portions of the circuit connected to the series winding 20 will have a certain alternating current potential-with respect to ground. Because of this capacity efiect between the series winding 2O and line windings 20 of the hybrid coil 20, as indicated by the dotted condensers between the windings, there will be a stray path for alternating currents between the output circuit of tube 21 and the common filament circuit for tubes 21, 22,- 21 and 22, 1

this path being traced from the series winding 20 of hybridcoil 20, through the capacitive path between that winding and the line windings 20 and over the bridge connections of hybrid coil 20 to potentiometer 25, the ground connection thereto, ground connection 41 to k the commonfilament circuit tortubes 21, 22, pli fiers'21 and 22 21 and 22, as indicated by the dotted lines, tocathode 27 of tube 21, space path of tube 21 to series winding 20 of hybrid coil 20.

It has been found that in repeater systems in which hybrid coil transformers of the prior art are used, such as those illustrated in the circuit of Fig. 3, when talking currents are beingtransmitted through one repeating path, the mutual capacities between the windings of the hybrid coil in the output of that path andbetween the windings and ground are of appreciable value. Because of this mutual capacity. effect, leakage. alternating. current? willibetransmittedfrom the outputof the am-- plifier tube; in one. repeating path over the:

path tracedabove to the. common filament cir-n cuit. for. the several amplifier tubes. This leakagescurrent maybe suflicient to cause 1ap+ preoiable cross-talk disturbance in the circuits ofL thexamplifier tubes in theoppositely directed repeating path of the same repeater or l'in-the circuits of the amplifier tubes intlie repeating paths. of the neighboring repeater. This cross-talkdisturbance may be reduced or substantially eliminated in. accordance.

with the invention by employing-in the-sys-r lIGIDzOf Fig. 3Jhy brid coil transformers constructed to have low mutual capacities between windings and between windings and:

groiu1d,.such as, for example, the specially designed hybrid coil 20 illustrated'inFigJl.

Referring to. F ig. 4, hybrid coil ries winding 20,

comprises a multi-layer seand line windings 20.. each of which may comprise asingle layer. The.

series winding 20.," may. have any desired number'of. superposed layers which may. be:

wound in the manner similar to that illustrated for the multi-layer primary winding 6"of= transformer 5 in Figs. 2 and 5, on one leg of a shell. typecore, the line windings Q QO f being wound onthe core Asillustrated in layer series winding 20., of coilQO may be \VOUDdzOIl the-core so as to comprise anouter layer 43-which is nearest to the line wind- Wing-S2051, an intermediatelayered; and; an:

innen layer 45 farthest from the line windings-20 By constructing the hybrid coil transformer 20 in this way, the number of turns of the series windingQQ-f adjacentto Fig. 4, the. multi the. lower potential line winding 20 is re-- duced,. thus: reducing the mutual capacity; between the windings of the hybrid coiland therefore the stray alternating current trans-V mittedover the capacitive path. Theleakage alternatingcurrent transmitted from the output oftube 21 to the common filament. circuit for. the several amplifier tubes over the pathtraced above in connection with the system ofIFig; 3,- will be correspondingly re- 0 duced, thus decreasing the variations in the out-put currents of. the several amplifier tubes due to thiscause.

The stray alternating currents-transmitted from the output of amplifier 21 tothe circuitsofthe other amplifier tubes=22, 21 and 22 over the path traced above may be further reduced by concentrating the mutual capacity between-series winding 20 and'line windings 20 between points of minimum.

difference of alternating current" potential;

Thisis accomplished as indicated in Fig. 4 by connecting the terminai of the inner layer of series. winding 20.. which is farthest fizonrthe. line WindingsQO to a highialternat-ing current potential'point in the output.

it will be seen: that! other legs of the M QM circuit of tube- 21, fen: example; directly to the plateflSof; tliatwtube; ,andby; connecting thet'erininal of the' outenlayer 43.0f1serieswinding; 20,,{ w-hioh; is nearest: to the; line win ingsQOa-Q .tmai, point oflowerr alternating current-.petentialin ltheioutpnt. circuit of. tube 21, for example, to the midpoint of theifilament127 of-t11bef28a By. thisameans low potential-dine Winding,1205,'. is effectively. shield:

ed; from. the-high; potentialv layer 45. of the series-wvinding.20 f bywlayersv l l andv 45 of Winding, 20 whichlareof lower alternating current. potential. This substantially re duces the; eflfectives-difi'erence of alternating current; potential! between the adj acentportionsof the'highand low windings of the hybrid; coil and, therefore, the amount of stray current transmitted over the capacitive path therebetwcen.

The aboyemethods, as well asthe additional methods .described in connection. with transformerifil .combinations of. these methods, or any othen-suitableconstruction, may be utilized; in designing; the: hybridcoils 19, 20, .19 and20 sei-as'to substantially eliminate the effectiof the. mutual; capacity between the. windingsofi the hybridcoils and between thewyindings: and: ground,, and thus to reduce. the stray. alternating current. passing, frontthe' outputcircuit of one tubezthrough the" associated hybrid coiltransformer and ground: connections to, the common filament circuiu tonmamounta which,will. be too small toacause; serious; crosstalk interference in the-circuitsof the other amplifier tubes.

Vhile the invention.hasbeen described as embodied-inispeciahtnansmissionand repeating. systems, and. in connection. with. output transformers: therein, it: is. apparent that. it is-not limited .to.the systems.- described' or to output transformers, butmay, be'employed in 1 other. systemscomprising: circuits .employingI transmission apparatus having a. capacitive. effect: between. its elements at. different potentials.- and, between. its; elements. and. ground, and: having. leakage paths for. alternating. cunrentsbetween. thezcircuits, without departing from the-spiritand scope of the. invention as defined in; the. appended claims.

What is. claimed is 1 In combination, a. source. of" alternating current waves, a. circuithaving a. primary portion connected. toisa-i'd' source, and a secondary portion, a transmission. device comprising.- elements respectively connected to and. coupling. said primary. portion and said secondary portion. of'said circuit for a desired) transmission! of said waves. therebetween said d eviee providing a. leakage pathfor alternating, currents between. said primaryportionl and said. secondary portion. of said circuit, ,a secondlcircuit for transmitting electrical waves and coupled respectively to saidiprimary. portionand .saidsecondary portion of the first mentionedcircuit; through 3 leakage paths for alternating;currents,.and means inherent insaid device for reducing the amount of leakage, alternatinmcurrent cuit aiidsaid second circuit over saidleakage path including means .for substantially reducing the amount of alternating current transmitted between said primary portion therebetween.

2. A combination in accordance with that of claim 1, and in which one element of said transmission device connected to the primary portion of said first-mentioned circuit com-V prises several sections only one of which is in close proximity to an element of said device connected to the secondary portion of said first-mentioned circuit. 3. A combination in accordance with that; of claim 1 and in which an element of said transmission device of low alternating current potential is shielded from the portions of another element of said device of higher potential by portions of said other element of intermediate potential.

4. A combination in accordance with that; of claim 1 and in which said transmission device comprises a transformer having a priiiiary windin connected to the primary portion of said first-mentioned circuit and a sec-1f ondary winding connected to the secondary,

portion thereof, and said means included in said transformer for substantially reducing the amount of alternating current transmitsecondary portion of said first mentioned, circuit comprises means forreducing the niutual capacities between said primary and secondary portions to a negligible value.

5. In combination, a circuit for transmitting alternating electrical currents and having a primary portion and a secondary portion, a transformer comprising windings re 7 spectively connected to and inductively cou-' pling said primary and said secondary por-; tions of said circuit, a second circuit for transmitting electrical currents, coupled to the secondary portion of .the first-mentioned,

circuit through a leakage path, and a path for alternating currents between said second circuit and the primary portion ofsaid firstmentioned circuit, said transformer including means for reducing the transfer through 1 said leakage path of alternating currents between said first-mentioned circuit and said? second circuit due to the capacitive coupling therebetweeii. 6. A combination in accordance with that of claim 1, and in which said transmission de vice comprises a transformer having a prii'narywinding connected to said primary por.- tion of said first-mentioned circuit anda secondary winding connected to the secondary vice.

acore and primary V :wound: thereon, said primary winding portion; of said first-mentioned circuit, said transformerincluding means for reducing the mutual capacities between itswindings .and between saidprimarywmding and sa d transmitted between the first mentionedcir- .nati g current potential between the windings and between the. windingsand said second circuit are substantially lowestlf and said secondary portion of said first-mentioned circuit dueto the capacitive coupling.

, combination in accordance with jthat of cla m 1 and m which said transmission device comprises a transformer having a core and windings mounted thereon including a primary. winding coniiectedto the primary portioniofrsaid first-mentioned circuit and secondary winding I :aryportion of said first-mentioned circuit,

connected to the secondsaid primary winding'comprising a plurality oflayers superposed on said core, said secwinding at an alternating current of {said primary windin 8. In comb nation, a plurality of space discharge devices, each having-a plate-or anode: and acathode or filament and an sin-" dependent direct current output circuit connected, between its plate and filament, the

filament ofsaid devices being fedin series from a. common heating source, a path for alternating; currents between the output cir cu'it of one of said devices and the common ted be'wcen said p imary portion and said heating circuit, and means for rendering the output circuit current of said one device substantially inefi'ective to cause variations in the clrcuit of another of sa d devices over said path.

, 9. In .comb inationpa plurality of space "discharge devices each having a filament and a plate, the. filaments; of said devices being energized in series from a commonsource, an output transformer comprising primary and secondary windingsconnected between the plate and filament ofone of said devices,

a path for alternating currents between said primary: winding; and the common filament circuit; and means inherent in said transformerfor preventing leakage due to the capacitive coupling :between said, alternating current path andthe output of said one device to the filament of another of saiddevices of sufficient current to cause appreciable disturbance in the circuit of said other de- 10. Inlcoinbination, a plurality of space discharge devices eachhaving' a filament and plate, energized the filaments of said devices being in series from a common current sourcegan- "oitputtransformer comprising and secondary windings being ing a cathode-filament connected in the outputcircuit of'oneof said 1 devices between the plate-and-"filament thereformer including means for "reducing the capacity couplingsbetween said ,outputcircuit and saidpath foralternat-ing currents sufficiently to prevent substantially ;any transfer of leakage alternating "current through the output transformer of said one device to the filamentofanotherofsaiddevices.

11. In a transmission system, a "pair of transmission lines, a repeater ci-rcuit'interconnecting said lines .and including oneway paths for transmitting in opposite directions between said lines, each "of said. paths including a space discharge amplifying device having. a cathode or filament and an anode or plate, thefilamentsof the space discharge devices in said paths'being supplied with energizing current in series from a common source, a transformer *comprising a .coreand primary and secondary was rents-and 'oversaid path to said common 'heating circuit for said filaments to cause disturbance --in the 'circuit of said second space discharge device.

ln' witness whereof, I hereunto subscribe myname-this 24th day of April, 1928.

KA'REL LUTOMIRS'KI.

windings wound thereon, said primary'winding being connected in'the output'circuitof one of said devices betweent'he plate and filament thereof, and a path for. alternating currentsbetween said secondary winding and the common filament. circuitfor saiddev'ices,' said transformer including means for reducing the effective mutual. capacities 'between said output circuitandsaid pathlfor alternating currents to value. sufiic'ientlylow 'as to prevent theleakage of suflicient alternating currentfromthe output ofsaid one amplifying device through the capacitive path to cause disturbance in the circuitof the other amplifying device.

12. In a transmission system, a repeater circuit including a space discharge device having a catho'de or filament and an anode or plate, and a transformer comprising a core and a primary Winding and a secondary Winding mounted thereon, said primary winding being connected intheoutput circuit of said device between ,theplate and filamentthereof, a second repeater circuit including a second space discharge device havand a plate or anode, the filaments of the first-mentioned space discharge device and said second space-discharge device being supplied with heating current in series from a common source, a p h for alternating currents between ithe said first-mentioned space discharge device over the capacitive :put circuit and;saidpathrfonalternatingcur- ;path between said cont- 

